Eye-protection device having dual high voltage switching

ABSTRACT

An auto darkening eye protection device comprising a shutter assembly and a control circuit. The shutter assembly is adjustable between a clear state and a dark state. The control circuit comprises a sensing circuit, a weld detect circuit, and a delivery circuit. The sensing circuit senses incident light and provides an output indicative of the incident light. The weld detect circuit receives the output of the sensing circuit, and enables a dark state drive signal to be delivered to the shutter assembly. The delivery circuit outputs the dark state drive signal to the shutter assembly to switch the shutter assembly from the clear state to the dark state upon enablement by the weld detect circuit. The dark state drive signal includes a high voltage pulse followed by a stable AC waveform. The high voltage pulse is formed by a positive voltage signal and a negative voltage signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. Ser. No. 10/139,837,filed on May 3, 2002, which claims priority to the provisional patentapplication identified by U.S. Ser. No. 60/288,760 and filed on May 5,2001, the entire content of both patent applications is hereby expresslyincorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an eye protection device constructed inaccordance with the present invention.

FIG. 2 is a schematic diagram of a control circuit constructed inaccordance with the present invention for controlling a shutterassembly.

FIG. 3 is a graph illustrating a positive voltage signal and a negativevoltage signal in accordance with the present invention.

FIG. 4 is a front perspective view of the eye protection device.

FIG. 5 is a rear perspective view of the eye protection device.

FIG. 6 is a rear elevational view of the eye protection device.

FIG. 7 is a side elevational view of the eye protection device.

FIG. 8 is a front elevational view of the eye protection device.

FIG. 9 is a second embodiment of a control circuit constructed inaccordance with the present invention for controlling the shutterassembly.

FIG. 10 is a third embodiment of a control circuit constructed inaccordance with the present invention for controlling the shutterassembly.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and in particular to FIG. 1, showntherein and designated by the reference numeral 10 is an eye protectiondevice constructed in accordance with the present invention. In general,the eye protection device 10 is designed to automatically darken in thepresence of an intense light, such as a welding arc. The eye protectiondevice 10 is preferably adapted to be worn by an individual. Forexample, the eye protection device 10 can be implemented in the form ofa cassette 11 (FIGS. 4-8) suitable for mounting in a welding helmet (notshown).

The eye protection device 10 is provided with a control circuit 12, anda shutter assembly 14. The shutter assembly 14 is an auto-darkeningfilter capable of being driven between a clear state and a dark state.In the clear state, an individual can see through the shutter assembly14 under ambient light conditions. In the dark state, the shutterassembly 14 becomes opaque so that the individual can only see throughthe shutter assembly 14 in the presence of an intense light, such as awelding arc.

The switching speed of the eye protection device 10 is an importantperformance attribute of the eye protection device 10. As will be wellunderstood by those skilled in the art, the switching speed is the timeperiod for switching the shutter assembly 14 from the clear state to thedark state. As will be discussed in more detail below, in accordancewith the present invention, a dark state drive signal having a highvoltage, e.g. 30 V, is provided to the shutter assembly 14 to enhancethe switching speed of the shutter assembly 14. The shutter assembly 14is preferably a liquid crystal display, such as a twisted nematic liquidcrystal display.

The control circuit 12 senses the intense light and outputs the darkstate drive signal to the shutter assembly 14 to cause the shutterassembly 14 to switch from the clear state to the dark state. If thecontrol circuit 12 senses that no welding arc is present, the controlcircuit 12 will cause a “clear state” drive signal to be delivered tothe shutter assembly 14.

In general, the control circuit 12 is provided with a power supply 16, apower regulation circuit 20, a sensor circuit 24, a weld detect circuit28, a positive voltage timer 32, a negative voltage timer 36, a positivevoltage generator 40, a negative voltage generator 44, a shade controlcircuit 46, a delay circuit 48, an oscillator circuit 52, and a deliverycircuit 56.

The power supply 16 includes a battery power supply 60, and a solarpower supply 64. The solar power supply 64 provides electrical power tothe sensor circuit 24 via a power line 68, and electrical power to thepower regulation circuit 20 via a power line 72. The battery powersupply 60 provides electrical power to the power regulation circuit 20via a power line 74.

In accordance with one aspect of the present invention, the powerregulation circuit 20 allows the solar power supply 64 to power thesensor circuit 24, and regulates any additional power from the solarpower supply 64 to be supplied to the remainder of the control circuit12. This additional power is preferably regulated from above the voltageof the battery power supply 60 so that the power generated by the solarpower supply 64 will be used before any power from the battery powersupply 60. This reduces the load on the battery power supply 60 andthereby extends the life of the battery power supply 60.

In general, the solar cell voltage that assists the rest of the controlcircuit 12 (non-sensor) must be limited to a predetermined voltage, suchas 6.4V. To do this, in one preferred embodiment shown in FIG. 2, lowcurrent Zenor diodes (Z1 and Z2) are used. These Zenor diodes (Z1 andZ2) need a minimum of 4 uA to 8 uA for their reference voltage to bestable at 1.22V each. For this to happen, first if the eye protectionunit 10 is in the clear state, the shade control circuit 46 is off and(if enough light is on the solar power supply 64) the current must comefrom the solar power supply 64. This is done through R14. If there isnot enough light the reference will not affect the shade. The secondstate is if the eye protection unit 10 is in the dark state. In the darkstate the reference must be accurate. Some solar power can be used, butto make sure the zenor diodes Z1 and Z2 have enough current throughthem, even at low light, additional current is supplied from the shadecontrol circuit 46 through R50. This will insure the zenor diodes haveenough current to maintain a stable voltage to the shade control circuit46 via a line 75 and thus a stable shade.

In accordance with the present invention, the regulation of the solarpower supply 64 can be implemented in other manners. For example, asshown in FIG. 9, an alternate circuit having a FET is utilized toregulate the solar power supply 64 to maintain the stable referencevoltage. As shown in FIG. 10, an op-amp circuit is utilized to regulatethe solar power supply 64 to maintain the stable reference voltage.

The battery power supply 60 can be provided with any suitable voltage soas to supply power to the control circuit 12 and the shutter assembly14. For example, the battery power supply 60 can be provided with avoltage in a range from about 2.0 V to about 6.5 V. In a preferredembodiment depicted in FIG. 2, the battery power supply 60 has about 6Volts.

The sensor circuit 24 detects the presence of light and outputs a sensoroutput signal representative of the level of light detected. The sensoroutput signal is output to the weld detect circuit 28 via a signal path76. The weld detect circuit 28 enables the drive signal that will bedelivered to the shutter assembly 14. In general, if the sensor outputsignal indicates to the weld detect circuit 28 that an intense light,such as a welding arc is present, the weld detect circuit 28 will causea dark state drive signal to be delivered to the shutter assembly 14. Ifthe sensor output signal indicates to the weld detect circuit 28 that nowelding arc is present, the weld detect circuit 28 will cause a “clearstate” drive signal to be delivered to the shutter assembly 14.

The dark state drive signal is provided with two components; a highvoltage pulse followed by a stable AC waveform. The high voltage pulsequickly drives the shutter assembly 14 from the clear state to the darkstate. The stable AC waveform maintains the shutter assembly 14 in thedark state. The high voltage pulse preferably has a voltage in a rangefrom about 15 V to about 120 V, and a time period from about 10microseconds to about 100 milliseconds. In general, the voltage of thehigh voltage pulse will depend on the maximum voltage ratings of thecomponents utilized to implement the control circuit 12. In onepreferred embodiment, the voltage of the high voltage pulse is about 30V, and the time period of the high voltage pulse is about 1 ms.

As shown in FIG. 3, the high voltage pulse is formed by a positivevoltage signal (referenced to ground) synchronized with a negativevoltage signal (referenced to ground). The positive and negative voltagesignals are labeled in FIG. 3 with the designations “PVS” and “NVS”. Inother words, the leading edges of the positive voltage signal and thenegative voltage signals are synchronized. The shutter assembly 14 doesnot have a ground reference, and therefore, does not differentiatepositive or negative. The voltage of the high voltage pulse in the darkstate drive signal is thus the difference between the positive voltagesignal and the negative voltage signal.

For example, if the positive voltage signal has a magnitude of +18Volts, and the negative voltage signal has a magnitude of −12 Volts, thevoltage of the high voltage pulse would be +18 V−(−12 V)=+30 Volts.

The positive voltage signal is produced by the positive voltage timer 32and the positive voltage generator 40. The negative voltage signal isproduced by the negative voltage timer 36 and the negative voltagegenerator 44.

The positive voltage timer 32 sets the time period of the positivevoltage signal. The positive voltage generator 40 produces the magnitudeof the positive voltage signal. Likewise, the negative voltage timer 36sets the time period of the negative voltage signal. The negativevoltage generator 44 produces the magnitude of the negative voltagesignal. In one preferred embodiment, the positive voltage generator 40triples the voltage of the battery power supply 60, and the negativevoltage generator 44 doubles the voltage of the battery power supply 60so that the high voltage pulse has a voltage 5 times the voltage of thebattery power supply 60. The positive voltage timer 32 receiveselectrical power (via a signal path 79) having the increased voltagefrom the positive voltage generator 40 so that the positive voltagetimer 32 can switch components in the positive voltage generator.

The advantage of using the positive voltage signal and the negativevoltage signal is that the cost of manufacturing the control circuit 12is reduced. That is, electrical components which switch over 18 Voltsare more expensive than electrical components which switch below 18Volts. By using the positive voltage signal and the negative voltagesignal only one more expensive and higher voltage part, i.e. thedelivery circuit 56, is needed to send a voltage higher than 18 Volts tothe shutter assembly 14.

When the sensor output signal indicates to the weld detect circuit 28that an intense light, such as a welding arc is present, the weld detectcircuit 28 outputs a signal to the positive voltage timer 32 and thenegative voltage timer 36 via signal paths 80 and 84 to cause thepositive voltage signal and the negative voltage signal to be fed to thedelivery circuit 56 via signal paths 88 and 92. That is, upon receipt ofthe signal from the weld detect circuit 28, the positive voltage timer32 and the negative voltage timer 36 output respective timing signals tothe positive voltage generator 40 and the negative voltage generator 44via signal paths 96 and 100. In response thereto, the positive voltagegenerator 40 and the negative voltage generator 44 output the positivevoltage signal and the negative voltage signal to the delivery circuit56. The delivery circuit 56 outputs the positive voltage signal to theshutter assembly 14 on a signal path 104, and the negative voltagesignal to the shutter assembly 14 on a signal path 108 to cause theshutter assembly 14 to switch from the clear state to the dark state.

Then, the weld detect circuit 28 outputs a signal to the deliverycircuit 56 via the delay circuit 48 and signal paths 112 and 116 tocause the delivery circuit 56 to enable the stable AC waveform to theshutter assembly 14. The stable AC waveform maintains the shutterassembly 14 in the dark state. The stable AC waveform maintains theshutter assembly 14 in the dark state. The stable AC waveform ispreferably a squarewave having a user adjustable magnitude varying froma maximum of about +3.2 V-+4 V to a minimum of about −3.2V-−4 V. Thestable AC waveform can be provided with other shapes, such as asinusoidal shape, however, the efficiency of the circuit 12 will bereduced.

The stable AC waveform is produced as follows. The shade control circuit46 provides a stable DC voltage signal having a magnitude sufficient tomaintain the shutter assembly 14 in the dark state to the deliverycircuit 56 via a signal path 120. The oscillator circuit 52 provides anoscillating signal to the delivery circuit 56 via a signal path 124 tocause the delivery circuit 56 to produce the stable AC waveform. In onepreferred embodiment, the oscillating signal causes the delivery circuit56 to periodically switch the polarity of the signal transmitted to theshutter assembly 14.

If the sensor output signal indicates to the weld detect circuit 28 thatno welding arc is present, the weld detect circuit 28 will cause a“clear state” drive signal to be delivered to the shutter assembly 14via the delay circuit 48, the delivery circuit 56 and the signal paths112, 116, 104 and 108. The delay circuit 48 delays the submission of theclear state drive signal to the delivery circuit 56 for a predeterminedtime, thus preventing the shutter assembly 14 from switching to a clearstate during brief “off” periods in the weld pulsations that exist withvarious weld types. Further, once the welding arc is extinguished, thework piece which is being welded may glow brightly for severalmilliseconds thereafter. The delay circuit 48 delays the clear statedrive signal for desirably between about 0.1 seconds to about 1 seconds,and more desirably between about 0.2 seconds to about 0.4 seconds so asto protect the individual's eyes from the glow from the work piece. Thedelay circuit 48 may have a fixed time delay, or may be adjustable by auser so as to be set based on the user's preference.

In one preferred embodiment, the weld detect circuit 28 switches powerto the oscillator circuit 52 and the shade control circuit 46 via asignal path P1 to conserve battery power. That is, in the preferredembodiment, the oscillator circuit 52 and the weld detect circuit 28 areonly enabled when the weld detect circuit 28 senses the welding arc.

Shown in FIG. 2 is a schematic diagram of one preferred implementationof the control circuit 12.

Referring now to FIG. 4, shown therein is a front perspective view ofthe eye protection device 10. The sensor circuit 24 of the eyeprotection device 10 includes a pair of spatially disposed lightdetectors, such as phototransistors D10 and D11, for sensing the weldingarc.

The eye protection device 10 can be provided with a plurality ofcontrols for controlling various settings thereof. For example, as shownin FIG. 5, the eye protection device 10 can be provided with a firstknob 200 and a second knob 202 for adjusting the sensitivity and theshade of the eye protection device 10. The first and second knobs 200and 202 can be connected to any suitable component for adjusting thesettings of the eye protection device 10. For example, the first andsecond knobs 200 and 202 can be connected to potentiometers.

FIG. 5 is a rear perspective view of the eye protection device.

Referring now to FIG. 2, one embodiment of the control circuit will bedescribed. The sensor circuit 24 includes one or more phototransistorD10 and D11 with the output of each phototransistor D10 and D11 coupledto feedback circuits 206 a and 206 b. The construction and function ofthe phototransistors D10 and D11 are similar. Likewise, the feedbackcircuits 206 a and 206 b are similar. Thus, only the phototransistor D10and the feedback circuit 206 a will be discussed hereinafter forpurposes of brevity.

The output of phototransistor D10 is sent to line 208. A load resistorR40 is connected between line 208 and ground. Additionally, a capacitorC8 couples line 208 to line 209. Resistor R10 is connected between line208 and ground. Line 209 is also connected to the noninverting input ofamplifier 210. Amplifier 210 is preferably configured as closed loopnoninverting amplifier wherein the resistors R34, R33, R44 and R21 forman adjustable feedback loop connected to the inverting input ofamplifier 210 as shown. In particular, R21 is adjustable to permit thesensitivity of the sensor circuit 24 to be adjusted. The output ofamplifier 210 on line 76 serves as the sensor circuit output. Line 76 isconnected to the input of the weld detect circuit 28.

The solar power supply 64 powers the phototransistor D10 and amplifier210 via line 68. Thus, if the solar power supply 64 is left unexposed toincident light, phototransistor D10 and amplifier 210 will not receivepower, thus preventing the phototransistor D10 and amplifier 210 fromdraining the battery power supply 60 when the welding helmet is not inuse (when not in use, the welding helmet is typically not exposed tointense light).

The feedback circuit 206 a for the phototransistor D10 comprises aresistor capacitor circuit 216 connected between the emitter of thephototransistor and ground, and a feedback transistor Q5 having a basecoupled to line 218 of the resistor capacitor circuit 216, a collectorcoupled to the base of the phototransistor D10, and an emitter coupledto the ground via resistor R42.

Phototransistor D10 serves as the weld sensor. It receives an input ofincident light 220 and produces an output on line 208 representative ofthe intensity of the incident light. The phototransistor D10 used in thepresent invention is preferably a planar phototransistor configured fora surface mount. The planar phototransistor is smaller than conventionalmetal can phototransistors, thus allowing a reduction in size of theunit in which the sensor circuit is implemented. While the metal canphototransistors used in the sensor circuits of the prior art had athickness of about {fraction (1/2)} inch, the planar phototransistorswith a surface mount used in the present invention have a thickness ofonly about {fraction (1/4)} inch. This reduction is thickness allows thesensor circuit to be implemented into a smaller and sleeker unit.Further, the surface mount configuration of the phototransistor D10allows the phototransistor to be easily affixed to a circuit board. Theinventor herein has found that the TEMT4700 silicon npn phototransistormanufactured by Vishay-Telefunken is an excellent phototransistor forthe present invention as it has a smaller size than conventional metalcan phototransistors and allows the sensor circuit to maintain aconstant signal level without excessive loading or the drawing ofexcessive current.

The resistor capacitor circuit 216 and the feedback transistor Q5 in thephototransistor feedback circuit 206 a function to adjust thesensitivity of the phototransistor D10. The resistors R30 and R8 andcapacitor C15 are chosen to be of a size to provide a relatively largetime constant, and therefore a relatively slow response to changes involtage on line 208. The delay exists because of the time it takes forthe voltage on line 218 to charge to an amount sufficiently large toactivate Q5. Exemplary values for R30 and R8 are 1 MΩ and 2 MΩrespectively. An exemplary value for C15 is 0.1 μF. A detaileddescription of the operation of the resistor capacitor circuit 216 andfeedback transistor Q5 can be found in prior U.S. Pat. Nos. 5,248,880and 5,252,817, the disclosures of which have been incorporated byreference.

The signal on line 208 if fed into the amplifier 210. The signal isfirst passed through a high pass circuit formed by capacitors C8 and C9to block the DC component of the detected signal. Line 209 contains theDC blocked detected signal. The current on line 209 is diverted toground via resistor R10.

The sensor circuit 24 operates in the presence of both AC welds and DCwelds. In an AC weld (also known as a MIG weld), the welding light ispulsating. Thus, the phototransistor D10 will detect a pulsating lightsignal. The frequency of the pulsations is often 120 Hz. In a DC weld(also known as a TIG weld), the welding light is substantiallycontinuous, with the exception of a small AC component. When an AC weldis present, the phototransistor will produce a pulsating output on line208. The variations in the voltage signal due to the pulses will bepassed through the capacitors C8 and C9 to line 209 and fed into theamplifier 210. The amplifier 210 will then provide gain for the signalon line 209 which is sufficient to trigger the delivery of the “darkstate” drive signal to the shutter assembly 14.

When a DC weld is present, the phototransistor D10 will quickly producean output on line 208 catching the rising edge of the DC weld. Thissudden rise in voltage on line 208 will be passed through to theamplifier 210 causing a signal on line 76 sufficient to trigger thedelivery of a “dark state” drive signal to the shutter assembly 400.Thereafter, capacitors C8 and C9 will block the DC component of the DCweld, allowing only the AC variations in the DC weld to pass through tothe amplifier 210. A non-reactive element, e.g., resistor R49, ispositioned in parallel with the high-pass filter circuit formed by thecapacitors C8 and C9. The non-reactive element provides a DC bias to theinput of the amplifier 210 to aid in the detection of the DC weld. Thatis, the brighter the light being generated from the weld becomes, themore sensitive the sensor circuit 24 becomes. In one embodiment, R49 canhave a value of 10 M ohm.

The amplifier 210 can be a closed loop, noninverting amplifier asdescribed above. The amplifier 210 can be provided with a feed-back loopformed by R34, R33, R44 and R21. R21 is preferably an adjustableresistor so that the gain of the amplifier 210 and thus the sensitivityof the sensor circuit 24, can be adjusted by the user. Suitable valuesfor R34, R33, R44 and R21 have been found to be 1 M ohm, 2 M ohm, 392 kohm and 1 M ohm.

The sensor circuit 24 is also provided with an OR logical circuit 224receiving the outputs from the circuits 206 a and 206 b. The OR logicalcircuit 224 permits the highest voltage level from the circuits 206 aand 206 b to be passed.

The output of the amplifier 210 is fed into the weld detect circuit 28.The weld detect circuit 28 is provided with an electronic switch, anexample of which is shown in FIG. 2 as the FET Q9, a delay circuit 230and a switching circuit 232.

The delay circuit 230 can be formed of a RC circuit and serves toprevent inadvertent switching of the shutter assembly 14 from the darkstate to the clear state. That is, the light received by the sensorcircuit 24 from the welding arc can be a pulsating signal caused bysputtering of the weld. When the amplifier 210 receives a signal ofsufficient magnitude, the output of the amplifier 210 goes high. Thehigh signal is fed to the gate of the FET Q9. FET Q9 then turns on andthereby shorts a capacitor C10 to ground. Once the intensity of thelight detected by the sensor circuit 24 decreases, capacitor C10 willbegin charging through R26 until the next pulse of intense light isprovided to the sensor circuit 24. Thus, the time period of the RCcircuit formed by the capacitor C10 and a resistor R26 is selected tomaintain the capacitor C10 in a “low” state between pulses to maintain astable low signal to the switching circuit 232.

The “low” signal is provided to a switch input “C” of the switchingcircuit 232. This causes the switching circuit 232 to switch between theZ1 and the Z0 inputs. A high signal is applied to the Z0 input and theground reference is applied to the Z1 input. Thus, when the low signalis provided to the switch input “C”, a high signal is provided to thedelay circuit 48 via the signal path 112. The delay circuit 48 isprovided with an electronic switch as represented by transistor Q8, andan RC circuit as represented by R38 and C13. The high signal switches onthe transistor Q8 causing the capacitor C13 to charge. The delay circuit48 provides a time delay when the control circuit 12 switches from thedark state to the clear state. That is, when the welding stops theworkpiece is still glowing brightly. Thus, the time delay of the delaycircuit 48 is selected such that the user's eyes will be protected untilthe glow of the workpiece is diminished. The time delay of the delaycircuit 48 can vary widely based on user preference. However, suitabletime periods range from about 0.2 seconds to about 0.4 seconds. Suitablevalues for the resistor R38 and the capacitor C13 are 4.3 M ohm and0.047 micro farads.

The positive voltage timer 32 is formed by resistors R23, R48,transistor Q10 and capacitor C20. The negative voltage timer 36 isformed by resistors R28, R35, transistor Q7 and capacitor C11. Thepositive and negative voltage timers 32 and 36 serve to properly biasthe inputs of the positive and negative voltage generators 40 and 44 togenerate the high voltage pulse.

The emitter of the transistor Q8 is connected to the capacitor C12 viathe line 116. The capacitor C12 is connected to the base of transistorsQ7 and Q10. The transistors Q7 and Q10 short the capacitors C11 and C20,which then have to recharge causing the time frame in which the positiveand negative voltage generators 40 and 44 produce the high voltagepulse. This also causes low signals to be provided to switching circuitsU4 and U5 via lines 96 and 100.

The positive voltage generator 40 is also provided with at least twocapacitors C2 and C3, and a directional control circuit 244. Theswitching circuit U4 has a plurality of switches X, Y and Z forswitching the positive voltage generator between a charging state and adischarging state. Each of the capacitors C2 and C3 are connected to theswitching circuit U4 and a reference voltage to establish charging ofthe capacitors C2 and C3 in the charging state of the switching circuitU4.

Upon receiving the low signal from the positive voltage timer 32, theall of the switches of the switching circuit U4 switch to thedischarging state. In the discharging state, the capacitors C2 and C3are stacked to sum the voltage accumulated on the capacitors. That is, apositive lead of the capacitor C2 is connected to a negative lead of thecapacitor C3 through the switch X. Assuming that the voltage referenceis 6 V, this would cause a 12 V potential to exist across the stackedcapacitors C2 and C3. Further, the negative lead of the capacitor C2 isconnected to the reference voltage, e.g., 6 V, through the switch Y sothat the positive voltage signal, e.g., +18 V, exists from the groundreference to the positive lead of the capacitor C3. The directionalcontrol circuit 244 permits the flow of current between the negativeleads of the capacitors C2 and C3 and the reference voltage in thecharging state of the switching circuit U4, and prevents the flow ofcurrent between the negative leads of the capacitors C2 and C3 in thedischarging state of the switching circuit U4 so that the positivevoltage signal is generated. The positive voltage signal is thenprovided to the delivery circuit 56 via lines 248 and 88 through theswitch Z.

As shown in FIG. 2, in one embodiment the directional control circuit244 includes at least two diodes, as designated by the reference numeralD2. Although the directional control circuit 244 has been shown anddescribed as the diodes D2, it should be understood that the directionalcontrol circuit 244 could be implemented in other manners. For example,the directional control circuit 244 can be implemented as any devicehaving a P-N junction, such as a transistor, or an enhanced MOSFET.

The value of capacitors C2 and C3 can vary widely depending on the 1)output voltage, 2) load, and 3) length of time for the voltage to switchthe shutter assembly 14. For example, in one embodiment the capacitorsC2 and C3 can be 2.2 micro farad capacitors. The switching circuit U4 ispreferably 1) an integrated circuit having a plurality of electronicallycontrolled switches, or 2) separate electronically controlled switches.

The negative voltage generator 44 is constructed in a similar manner asthe positive voltage generator 40, except as discussed hereinafter. Thenegative voltage generator 44 is provided with a directional controlcircuit 250 permitting the flow of current between the negative leads ofthe capacitors C4 and C5 and the reference voltage in the charging stateof the switching circuit U5, and preventing the flow of current betweenthe negative leads of the capacitors and the reference voltage in thedischarging state of the switching circuit U5. Further, to generate thenegative voltage signal, the positive lead of the capacitor C4 isconnected to ground in the discharging state of the switching circuitsuch that the negative voltage signal is produced between the groundreference and the negative lead of the capacitor C5. The negativevoltage signal is output to the delivery circuit 56 through switch Z ofswitching circuit U5 via lines 252 and 92.

When the capacitors C20 and C11 have recharged, a high signal is outputto the positive and negative voltage generators 40 and 44 via the lines96 and 100. The high signal switches the switching circuits U4 and U5from the discharging state to the charging state to turn off thepositive and negative voltage signals.

Once the positive and negative voltage signals have been turned off, avoltage signal is transmitted to the delivery circuit 56 from the shadecontrol 46 through switch X of switching circuit U3 and via lines 256,120 and 88 to provide the stable AC waveform as discussed above.

As discussed above, in one preferred embodiment, the weld detect circuit28 switches power to the oscillator circuit 52 and the shade controlcircuit 46 via a signal path P1 to conserve battery power. That is, inthe preferred embodiment, the oscillator circuit 52 and the shadecontrol circuit 46 are only enabled when the weld detect circuit 28senses the welding arc. To enable the oscillator circuit 52 and theshade control circuit 46, the “B” input of the switching circuit 232 ofthe weld detect circuit 28 receives a signal on the line 116 when thehigh signal from the Z output of the switching circuit 232 switches onthe transistor Q8 causing the capacitor C13 to charge.

When the sensor circuit 24 no longer senses the welding arc, the signalon the line 116 switches to a “low” state thereby turning off thetransistor Q8. This permits the capacitor C13 to discharge through theresistor R38 causing a low state signal to be delivered on the line 116after a predetermined time period. The low state signal is received bythe “A” and “B” inputs of the switching circuit 232 and thereby causes a“low” state signal to be output by the “X” and “Y” outputs. This causesthe shutter assembly 14 to switch from the dark state to the clear stateand also disables power to the shade control circuit 46 and theoscillator circuit 52 to conserve battery power.

As discussed above, in accordance with one aspect of the presentinvention, the power regulation circuit 20 allows the solar power supply64 to power the sensor circuit 24, and regulates any additional powerfrom the solar power supply 64 to be supplied to the remainder of thecontrol circuit 12. This additional power is preferably regulated fromabove the voltage of the battery power supply 60 so that the powergenerated by the solar power supply 64 will be used before any powerfrom the battery power supply 60. This reduces the load on the batterypower supply 60 and thereby extends the life of the battery power supply60.

One skilled in the art will recognize that the present invention issusceptible to numerous modifications and variations. For example, theshutter assembly 14 and the control circuit 12 can be implemented in acassette connectable to a welding helmet, or integrated into the weldinghelmet. Further, the user controls can be on the cassette or separatefrom the cassette. For example, the user controls can be implemented asa “pig-tail.”

The embodiments of the invention discussed herein are intended to beillustrative and not limiting. Other embodiments of the invention willbe obvious to those skilled in the art in view of the above disclosure.

1. An auto darkening eye protection device comprising: a shutterassembly adjustable between a clear state and a dark state; and acontrol circuit comprising: a battery power supply having a voltage; asensing circuit sensing an occurrence of a welding arc and providing anoutput indicative of the occurrence of the welding arc; a weld detectcircuit receiving the output of the sensing circuit, the weld detectcircuit enabling a dark state drive signal to be delivered to theshutter assembly; a positive voltage generator generating a positivevoltage signal having a voltage higher than the voltage of the batterypower supply; and a negative voltage generator generating a negativevoltage signal, the positive voltage signal and the negative voltagesignal cooperating to form a high voltage pulse in the dark state drivesignal.
 2. The auto darkening eye protection device of claim 1 whereinthe positive voltage signal and the negative voltage signal are eachreferenced to ground.
 3. The auto darkening eye protection devicewherein the high voltage pulse has a voltage in a range from about 15 Vto about 120 V, and a time period from about 10 microseconds to about100 milliseconds.
 4. The auto darkening eye protection device of claim1, wherein the leading edges of the positive and negative voltagesignals are synchronized.
 5. The auto darkening eye protection device ofclaim 1, wherein the positive voltage generator includes: a switchingcircuit having a charging state and a discharging state; at least twocapacitors, each of the capacitors connected to the switching circuitand a reference voltage to establish charging of the capacitors in thecharging state of the switching circuit, and a positive lead of onecapacitor electrically connected to a negative lead of another one ofthe capacitors in the discharging state of the switching circuit; adirectional control circuit connected to the capacitors to permit theflow of current between the positive leads of the capacitors and thereference voltage in the charging state of the switching circuit, and toprevent the flow of current between the positive leads of the capacitorsand the reference voltage in the discharging state of the switchingcircuit.
 6. The auto darkening eye protection device of claim 5, whereinthe directional control circuit includes at least two diodes.
 7. Theauto darkening eye protection device of claim 1, wherein the negativevoltage generator includes: a switching circuit having a charging stateand a discharging state; at least two capacitors, the capacitorsconnected to the switching circuit and a reference voltage to establishcharging of the capacitors in the charging state of the switchingcircuit, and a positive lead of one capacitor electrically connected toa negative lead of another one of the capacitors in the dischargingstate of the switching circuit; a directional control circuit connectedto the capacitors to permit the flow of current between the negativeleads of the capacitors and the reference voltage in the charging stateof the switching circuit, and to prevent the flow of current between thenegative leads of the capacitors and the reference voltage in thedischarging state of the switching circuit.
 8. The auto darkening eyeprotection device of claim 7, wherein the directional control circuitincludes at least two diodes.
 9. An auto darkening eye protection devicecomprising: a shutter assembly adjustable between a clear state and adark state; and a control circuit comprising: a sensing circuit sensingan occurrence of a welding arc and providing an output indicative of theoccurrence of the welding arc; a weld detect circuit receiving theoutput of the sensing circuit, the weld detect circuit enabling a darkstate drive signal to be delivered to the shutter assembly; and adelivery circuit outputting the dark state drive signal to the shutterassembly to switch the shutter assembly from the clear state to the darkstate upon enablement by the weld detect circuit; and a power supplysupplying power to the control circuit and the delivery circuit, thepower supply comprising: a power regulation circuit; a solar powersupply supplying electrical power to the power regulation circuit andthe sensing circuit, the power regulation circuit limiting the voltageof the solar power supply to a predetermined voltage to provide a stablereference voltage.
 10. The auto darkening eye protection device of claim9, wherein additional current is provided to the power regulationcircuit when the control circuit is in the dark state.
 11. The autodarkening eye protection device of claim 10, wherein the power supply isprovided with a battery power supply in circuit with the powerregulation circuit, the power regulation circuit only utilizing orsupplying power from the battery power supply when the control circuitis in the dark state.
 12. The auto darkening eye protection device ofclaim 11, wherein the power regulation circuit includes at least twozenor diodes for maintaining at least two different referencepotentials.
 13. The auto darkening eye protection device of claim 11,wherein the power regulation circuit includes a FET regulating the solarpower supply to maintain the stable reference voltage.
 14. The autodarkening eye protection device of claim 11, wherein the powerregulation circuit includes an operational amplifier regulating thesolar power supply to maintain the stable reference voltage.